Rheostat.



PATENTED AUG. 6, 1907.

l E. F. NORTHRUP.

v RHEOSTAT.

APPLIUATION FILED MAY 3, 1907.

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UNITED STATES PATENT oEEioE.

EDWIN F. NOR'IHRUP, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TO THE LEEDS AND NORTHRUP COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENN- SYLVANIA.

RH'EOSTAT.

Specification of Iletters Patent.

Patented Aug. 6, 1907.

Application led May 3,1907. Serial No. 371,674.

in Rheostats, of which the following is a specification.

This invention relates to rheostats of the slide-wire type in which variation in resistance is'obtained by moving a contact over and in engagement with a resistance conductor, but is directed more especially to the form and construction of the resistance conductor proper and the manner of mounting or supporting the In order to more fully describe my said invention reference will be had to the accompanying drawings wherein,

Figure 1, is a central vertical section partly in elevation of one form of my rheostat; Fig. 2, a top plan view thereof, partly in section and with a portion broken away; Fig. 3, an enlarged detail view in elevation of a portion of the spiral conductor; Fig. 4, an enlarged cross section partly in elevation of said spiral conductor; and Fig. *5, a cross section partly in elevation of a rheostat embodying a modified form of my invention.

A rheostat embodying my invention may be constructed as follows:

Insulation covered resistance wire, consisting pref- .erably of silk-covered manganin wire, is wound in spiral formation of a desired length on a drill rod` or other suitable core, in a lathe or otherwise, with the adjacent turns of the spiral close together. The rod or core on which the wire is wound may be of any suitable diameter and the wire of a size dependent upon the resistance, mechanical strength etc., desired. The rod on which the wire is wound may be', for example,

anywhere from g to inch or more in diameter. For

general purposes a #52 rod and #3l manganin single silk-covered wire have been found satisfactory. For resistance thermometer and other work where very small graduations of resistance are desired, the wire may be extremely fine, the present construction permitting of the use of this extremely ine wire without sacrificing mechanical strength. After the wire is thus wound on the rod or core the latter` is pulled out of the spiral, leaving the spiral hollow. The spiral is then placed in a recess in'a suitable support and shellacked in place, and after the shellac has become thoroughly dry the insulation is buffed 0H the spiral in such manner as to leave a lengthwise portion thereof bare to form a contact surface. Other suitable binding agents may be substituted or shellac if desired. The form' of this support and the exact manner of mounting the coil herein may vary. In the form of my invention shown in Figs. 1 and 2, this support consists of a disk 1 o wood or otherinsulating material having an annular groove 2 in its periphery and in this groove is placed the resistance spiral conductor 3 l which is shellacked in place in said groove and after the shellac has thoroughly dried the insulation is taken off the exterior of the coil l ngthwise thereof as at 4, by a small buff or otherwise, the said bared portion forming a contact surface for the moving Contact K 5, which may be mounted on any `suitable arm 6, secured to a spindle 7 for operation by a knob 8. The

'disk 1 may be attached to any desired support such as the top 9 of an inclosing case 10.

Another way of mounting the spiral resistance coil is shown in Fig. 5. In this case a circular recess 11 is sunk into one face of a block l2 of wood or other insulating material, and the spiral conductor 3/ laid in said recess with the outer periphery of the spiral engaging the side walls of the recess. After this, a holding device consisting in the case shown of a circular block or disk 13 having a tapering periphery 14 is placed in position within the circle formed by the spiral conductor so that the tapering sides 14 of saiddisk will engage the inner periphery of the circular spiral formed by said conductor and thus coperate with the walls ofthe recess 11 to retain the said spiral resistance conductor in position. The disk 13 is held in position by being mounted upon an exteriorly screw-threaded plug 15 which passes upward through the block 12 and is held from rotation therein by a pin 16. the disk 13 being provided with a central interiorly screw-threaded opening 17, which engages the screw threads of the plug 15. By mounting the disk 13 as shown, the same may be screwed down into position and its sides firmly wedge the spiral resistance coil into place. The hollow plug l5 also acts as a sleeve for the rotatable spindle 18, to which is secured a Contact arm 19 of any desired form. In the drawings this arm is represented as being made up of a series of conducting strips bent at right angles at each end and adapted to engage at one of said ends the bared portion 4 of the Coil 3, and at the other end a Contact ring 20 of conducting material made fast to the disk 13. A binding post 21 forming one of the terminals of the rheostat may be Connected to the ring 20, asshown. Any suitable knob 22 or other device may be employed for operating the Contact arm 19.

The resistance conductors 3 and 3 are the same in every respect except that the conductor 3 is bared of insulation on the outer periphery of the circle formed by the `spiral Whilein the case of the conductor 3 the One of the great advantages gained by this form oi slide-Wire rheostat is that it enables us to obtain an extremely wide range oi resistance in a very small space by an arrangement which is extremely simple7 and at the same time mechanically very strong. It will be Observed that the spiral conductor is absolutely hollowthat is to say, it is wound on no form of core whether this-core be solid or in the form of a tube, and for this reason a maximum amount of ventilation is permitted and heat effects correspondingly reduced. As an example of the extreme compactness and Wide range of resistance rendered possible by such a construction, resistances varying from Zero to a couple of hundred ohms may be secured by a spiral conductor arranged in` a circle of only six inches in diameter, A single Wire Wound on a six inch circle giving the same resistance would be so extremely fine that its liability to get broken, Worn or loose would render it greatly inferior to the present arrangement.

Having thus described my invention, What I claim is:

1. A rlieostat, comprising an insulated electrical conductor spirally wound and forming a hollow coreless tube` the said tube having an exterior lengthwise portionbare of insulation, and a support having a recess in which said tube is laid sidewi'se, the said tube being supported wh'oll y from the outside.

2. A rheostat, comprising an insulated electrical cohductor sp'irally wound and forming a hollow coreless tube, the said tube having an'exterior lengthwise portion bare of insulation, a support having a recess in which said tube is laid sidewise, and aucompound forming a binding agent between adjacent convolutions of said spiral and between said tube and said support, the said tube being supported wholly from the outside.

3. A rheostat, comprising a hollow tube composed of a series of convolutons of an insulated spiral conductor, a supporting base having a'recess in which said tube is laid sideWise, and a holding block attached to said base and removable with respect thereto, said holding block adapted to coperate with the walls of said recess to retain said coil in position.

4. A rheostat, comprising an insulated spiral resistance conductor disposed in circular form, a supporting block having an annular recess in which said circular spiral is laid sidewise,v the peripheral walls of said recess engaging the outer periphery of the circular spiral, and a circular holding block having a tapering periphery adapted to engage the inner periphery of said circular spiral to cooperate with the walls of said recess to retain said spiral conductor in position. l

5. A rheostat, comprising an insulated spiral resistance conductor disposed in circular form, a supporting block having an annular recess in which said circular spiral is laid sidewise, the peripheraLwalls of said recess engaging the outer periphery of the circular spiral, and a clamping device adapted to coperate with the walls of said recess to hold said circular spiral in position, the clamping device and supporting block engaging said spiral and act-A ing to support and clamp the same wholly from the out side.

G. The improvement in .rheostats which consists in winding an insulation-covered resistance wire in close spiral formation on a core, withdrawing said core from said spiral, placing said spiral sidewise in a recess in a support, applying to the exterior of said spiral and to portions of said support adjacent thereto an insulating' compound forming a binding agent, and bui-ling Va portion of the insulation oft said spiral conductor lengthwise thereof to form a Contact surface.

In testimony whereof I affix my signature in presence of two Witnesses.

EDWIN F; NORTl-IRUI' Witnesses:

A. DE PREFONTAINE, HAROLD BANKEN. 

